The invention relates to a shearing machine for severing parallel longitudinal members of grids or gratings, the machine having a horizontal guide-beam which is stationary during the cut and upon which are provided counterbutts in the manner of comb teeth; and a cutter-beam which is movable parallel to and alongside the guide-beam during the cut and upon which blades are provided in the manner of comb teeth, the blades cooperating with the counterbutts on the guide-beam to shear longitudinal members extending through notches formed between adjacent counterbutts of the guide-beam and between adjacent blades of the cutter-beam. Such a machine is hereinafter referred to as of the kind described.
Amongst "grids" are to be understood systems of families of longitudinal rods parallel with one another and cross-rods parallel with one another, which cross one another and which are connected, in particular welded together, at the points of intersection. Amongst "gratings" are on the other hand to be understood systems which consist of a family of flat steel straps standing on edge in parallel with one another and a family of round rods parallel with one another which cross these straps at right angles and which are welded into a narrow side of the flat steel straps up to a depth corresponding with their diameter.
In the case of a known shearing machine of the kind described (cf. West German O.S. No. 2,439,185) the cutter-beam is movable relatively to the guide-beam by means of a double-acting working cylinder. The guide-beam is provided with counterbutts arranged in the manner of comb teeth at equal spacings, which exhibit sidefaces running on one side essentially perpendicular to the longitudinal extent of the guidebeam and supporting during the cut the longitudinal members of the grid or grating, which is to be severed. The cutter-beam likewise exhibits blades arranged in the manner of comb teeth, which have sidefaces standing at one side essentially perpendicular to the longitudinal extent of the cutter-beam and forming cutting edges, and which during the cut cooperate with the counterbutts.
But in contrast to the counterbutts on the guide-beam the blades on the cutter-beam are not equally spaced but are arranged at different spacings in such a way that the longitudinal members of the grid or grating get cut only individually or in groups in succession.
A shearing machine so constructed has on the one hand the advantage of managing with a small driving force since there is always only one individual longitudinal member (rod or strap) being severed or a group of only a few longitudinal members simultaneously, but on the other hand it has the disadvantage that those longitudinal members which are cut first get more or less sharply bent by the blades severing them, because the grid or grating respectively is still being held together at the longitudinal members not yet severed and therefore no part of it can follow unimpeded the motion of the blades. The motion of the blades must be continued until even the last longitudinal member has been severed. In the case of machines constructed in that way the travel of the blades is therefore large, so that the longitudinal members cut first remain continuously in engagement with the blades associated with them or at least until they are bent over so far that they slide off the blades. Since the individual blades moreover come into use one after another, the deformations of the individual longitudinal members are in addition unequally large.
The wear on the blades is also large since at each cut it is always the same cutting edges that get loaded. This is particularly unwelcome because the rapid wear of the cutting edges demands a frequent exchange of the guide-beam and cutter-beam, on account of which these two beams must be connected to the driving mechanism on the one hand detachably and on the other hand also positively.
The exchange of the guide-beam and cutter-beam is a time-wasting operation which besides must also be carried out when grids or gratings having different spacings of the longitudinal members have to be cut one after another.